This invention relates to a yarn feeding apparatus for multi-feed knitting machines, in particular circular knitting machines.
It is known that with multi-feed knitting machines, i.e. machines whereon a knitted fabric is formed by means of needles arranged to pick up plural feed yarns from a number of cops, reels, or the like, the yarns are picked up from said cops or reels and fed to the needles through feed apparatuses, comprising each a wheel set for free rotation about its own axis and having a substantially cylindrical shaped surface whereon a yarn can be pressed and held by a belt having a smaller height than the wheel driven through a motor means. The belt movement causes the wheel to rotate and entrain the yarn from a respective cop, said yarn being accordingly fed at a preset rate to the respective needles, whereto it is released from the belt and wheel.
In the instance of circular knitting machines, wheels of this type are arranged in a circle at the machine top and the belt which drives them rotatively is a single closed loop configuration.
Feed apparatuses of the wheel type as outlined above are described, for example, in German Pat. Nos. 1 585 298 and 1 635 893.
It is a known fact that it is often necessary to take one or more yarns out of contact with the belt, by shifting the yarn in question along the wheel axis direction, to one side of the cited belt; the yarn is allowed to slip over the surface of the wheel which continues to be rotated by the belt no longer acting, however, on the yarn. This occurs, for example, when the stitch length of the knitting machine is to be changed, or when the type of fabric knitted on the machine is to be changed, or when a knitwork is to be produced which has stripes of different colors and one or more yarns of a given color must be left out of the knitwork being knitted.
Owing to the knitting machines being operated at a high speed, where it becomes necessary to discontinue the feeding of a given yarn, the yarn in question has to be removed very quickly from its position in the nip between the belt and related wheel. Each yarn feeding apparatus is provided with a movable yarn inlet arm which is guided to and from the contact area between the belt and wheel, and with a movable outlet arm on which the yarn leaving the apparatus is passed; this outlet arm is responsive to the tension of the outgoing yarn, thereby lowering the tension on the outgoing yarn results in a decrease of the pressure applied on said arm, which acts mechanically or otherwise on the inlet arm or feeding finger, which moves up and takes the yarn out of the pressure area of the belt onto the wheel. The movable outlet arm which is somewhat longer than the yarn inlet arm, and the yarn trained over the cited wheel is moved and guided through two eyes, made each rigid with each of the arms. The two arms are rigid with each other by the provision of a rotatable shaft carried on the wheel holder; as the yarn is being picked up, both arms are shifted toward the belt so as to retain the yarn under the belt in a substantially longitudinal attitude with respect to the belt. When the feeding of said yarn is to be discontinued, the displacement of the two arms pulls the yarn out of contact with the belt and respective wheel. As mentioned, feed apparatuses of this type are well known and are described, for example, in German Pat. Nos. 1,585,298 and 1,635,893; however, they have the disadvantage of requiring a comparatively long time from the moment when the movable outlet arm acts on the movable inlet arm to shift the yarn laterally with respect to the belt. That time period is governed by the time required, consequently for the displacement and bias force transmitted by the outlet arm, for the inlet arm to move from the inoperative position into the operative one, and viceversa, to move the oncoming yarn to the apparatus from out of contact into the nip under the belt, where it is held pressed against the wheel. In other words, the time involved to take the yarn into the nip between the belt and wheel or move it out of that position, will depend on the effort to be exerted on the yarn by the inlet arm and on the angle wherethrough said arm is to be moved.
With conventional appratuses, the yarn is led to the eye of the inlet arm from a substantially parallel direction to the wheel axis, so that the inlet arm must increase or reduce the amount of yarn picked up therfrom whenever its attitude is to be changed; since the oncoming yarn to the apparatus always tends to apply a pull on the arm with a significant force toward the point where the yarn comes from, it follows that the rotational movement is considerably hindered by the action exerted thereon by the yarn, the arm thus inducing a significant variation in the amount of yarn being fed during the arm moving step. This results in a decrease of the apparatus responsiveness to variations in the pressure exerted by the outgoing yarn on the outlet arm, and hence a relatively low readiness of the apparatus to react to the requirement of changing the yarn feeding conditions or stopping altogether.
Moreover, with conventional apparatuses, the yarn inlet arm is always located in the proximity of the adjacent belt free edge, whereas to cause the apparatus to put the yarn into and out of feed, a shaped member is provided having a sloping surface over which the oncoming yarn to the apparatus is caused to slide, it moving outward, and respectively under, the contact area between the belt and wheel.
This arrangement for moving the yarn out of knitting, or respectively into knitting, namely for feeding it to the opening machine or viceversa, is a time consuming one which does not allow the yarn feeding to the knitting machine to be discontinued or, respectively, initiated at the high rate which would instead be desirable.